### irradiance

(EMR power reaching a surface)

**Irradiance** is the amount of electromagnetic radiation (EMR) (quantified
by its energy) per unit time (i.e., power)
striking a surface per unit area, from any direction.
It is conceptually the sum of the intensity (i.e., radiance)
from all directions.
Typical units:

- W/m² (watts per meter-squared; SI units).
- ergs/s/cm² (ergs per second per centimeter-squared; CGS units).

**Spectral irradiance** is irradiance per wavelength
or frequency.

(*measure,EMR*)
**Further reading:**

http://en.wikipedia.org/wiki/Irradiance

**Referenced by pages:**

flux density

insolation

radiative flux

Solar Maximum Mission (SMM)

Upper Atmosphere Research Satellite (UARS)

watt (W)

Index